This invention relates to a transmission, and more particularly to a device for gradually increasing hydraulic pressure in a hydraulic fluid supply control circuit of the transmission for shifting vehicle speed through the utilization of respective hydraulically operated cylinder piston assemblies of clutches provided in the transmission.
Conventional devices for gradually increasing hydraulic pressure have means for gradually increasing hydraulic pressure including a cylindrical valve, a pressure regulating valve, and a quick return valve for gradually increasing the hydraulic pressure within the main hydraulic circuit under the control of the pressure regulating valve together with the cylindrical valve. However, since fluid in the main hydraulic circuit is always communicated with the pressure regulating valve, if there exists fluid resistance within the main hydraulic circuit when lack of the cylinder chambers of the hydraulically operated cylinder-piston assemblies is filled with hydraulic fluid, the hydraulic fluid is also communicated with the pressure regulating valve so that it takes longer for the hydraulic fluid to fill in the cylinder chamber, which is disadvantageous.
In order to overcome such a disadvantage, the present inventors have proposed a device for gradually increasing hydraulic pressure which shuts off the pressure chamber of a pressure regulating valve from a main hydraulic circuit until the cylinder chamber of a hydraulically operated cylinder-piston assembly is filled with hydraulic fluid, as shown in FIG. 1.
However, this prior device for gradually increasing hydraulic pressure has an orifice e between a passage b and the pressure chamber d of a pressure regulating valve c for preventing a pressure vibration at the means a for gradually increasing hydraulic pressure. Consequently, even if the transmission is shifted so that the cylinder chamber of a hydraulically operated cylinder-piston assembly f is filled with hydraulic fluid with the result that the pressure chamber d of the pressure regulating valve c is communicated with the passage b, the hydraulic fluid within the passage b is throttled by the orifice e, and the hydraulic fluid is therefore introduced gradually into the pressure chamber d of the pressure regulating valve c. As a result, the responsibility of the means a for gradually increasing hydraulic pressure is deteriorated at the time of starting a gradual increase of the hydraulic pressure so that peak pressure is produced in the hydraulic fluid supply control circuit of the transmission having a source of hydraulic pressure of large capacity immediately before the hydraulic pressure is gradually increased in the hydraulic fluid supply control circuit, as shown in FIG. 2 with the result that a shock occurs when the transmission is shifted.
Furthermore, as the peak pressure takes place as described above in the hydraulic fluid supply control circuit of the transmission, the fluid amount introduced through an orifice h of quick return valve g into a chamber i is increased so that cylindrical valve j is moved in a leftward direction relative to the drawing until the hydraulic pressure starts to gradually increase so that the load of a spring k is increased with the result that the hydraulic pressure at the time of starting to gradually increase the hydraulic pressure is disadvantageous.
It is, therefore, an object of the present invention to provide a device for gradually increasing in a hydraulic fluid supply control circuit of a transmission which eliminates the aforementioned disadvantages of conventional devices for gradually increasing hydraulic pressure in the hydraulic circuit of the transmission and which may provide fast shifting of the transmission.
It is another object of the present invention to provide a device for gradually increasing hydraulic pressure in a hydraulic fluid supply control circuit of a transmission which may reduce the shock normally occurring upon the shifting of a transmission.
It is still another object of the present invention to provide a device for gradually increasing hydraulic pressure in a hydraulic fluid supply control circuit of a transmission which may attenuate the hydraulic pressure vibration which normally occurs after the hydraulic pressure begins to be gradually increased in the hydraulic circuit of the transmission.
It is still another object of the present invention to provide a device for gradually increasing hydraulic pressure in a hydraulic fluid supply control circuit of a transmission which may shut off the main hydraulic circuit from a pressure regulating valve until the cylinder chamber of each of hydraulically operated cylinder-piston assemblies of clutches provided in the transmission is filled with hydraulic fluid and may not produce peak pressure immediately before the hydraulic pressure begins to be gradually increased.